Usually in order to measure user's heart rate, for example during sports exercise, a heart rate measurement belt is worn. This belt measures heart's electrical activity. It transmits a trigger signal or the like to a registering device. By counting the time interval between these trigger signals, user's heart rate can be determined and presented. Usually this trigger signal is transmitter in a form of alternating low frequency magnetic field, due to the simplicity of this kind of technology.
In order to implement the alternating low frequency magnetic field registering function to a registering device, a pickup coil is needed. This is of course an additional and extra component meaning extra board space, extra cost and/or increased complexity.
In a known solution dedicated pickup coils have been used to measure the magnetic field signal sent by the measurement belt. Such a known apparatus is disclosed in the closest prior art document U.S. Pat. No. 4,625,733. There is shown a system that describes a procedure, a measurement device, a transmitter and a receiver for telemetric measurement of heartbeat or ECG. The receiver is based on three specific coils therein. The registering coils are designed for accurate results, but as an assembly do not satisfy multipurpose device.